Bisazo ink-jet dyes

ABSTRACT

A bisazo dye of Formula (1) and salts thereof:   &lt;IMAGE&gt; Formula (1) in which R is H; R1 and R2 each independently is H, optionally substituted C1-4-alkyl or optionally substituted aryl; R3 and R4 are each independently -OC1-4-alkyl; R5 is H; R6 is COOH; and n is 1, 2 or 3. The dyes are useful for ink jet printing.

The present invention relates to bisazo dyes, inks and to their use in inkjet printing.

Inkjet printing is a non-impact printing technique which involves ejecting, thermally or by action of an oscillating piezo crystal, droplets of ink continuously or on demand from a fine nozzle directly onto a substrate.

According to the present invention there is provided a bisazo dye of Formula (1) and salts thereof: ##STR2## wherein: R is H;

R₁ and R₂ each independently is H, optionally substituted C₁₋₄ -alkyl or optionally substituted aryl;

R₃ and R₄ each independently --OC₁₋₄ -alkyl;

R₅ is H;

R₆ is COOH; and

n is 1, 2 or 3.

The dyes of Formula (1) may be in the free acid form as shown but are preferably in the form of a salt, more preferably in the form of a water-soluble salt. Preferred water soluble salts of Formula (1) are those of alkali metals, for example Li, Na or K salts, and ammonium or substituted ammonium salts. Especially preferred salts are volatile ammonium salts.

In one embodiment of this invention R₃ and R₄ are each independently --OC₁₋₄ -alkyl provided that R₃ and R₄ are not both --OC₂ H₅. In another embodiment R₃ and R₄ are both --OC₂ H₅.

When R₁ or R₂ is optionally substituted alkyl or aryl the optional substituents are preferably selected from --NHC₁₋₄ -alkyleneOH, --NHC₁₋₄ -alkyl, --(NH₂)C₁₋₄ -alkyl, --COOH, ##STR3## in which X is --NH or O.

Preferably R, and R₂ are each independently H, --CH₂ CH₂ NHCH₂ CH₂ OH, --CH₂ CH₂ NHC₁₋₄ -alkyl, --CH₂ CH(NH₂)CH₃, ##STR4##

In a more preferred embodiment one of R₁ and R₂ is H and the other is --CH₂ CH₂ NHCH₂ CH₂ OH, --CH₂ CH₂ NHC₁₋₄ -alkyl, --CH₂ CH(NH₂)CH₃, ##STR5##

Where R₁ or R₂ is aryl it is preferably phenyl.

Preferably n is 1.

The dyes of Formula (1) may be prepared by methods analogous to those described in the art for similar azo compounds. Thus, for example, a suitable method comprises:

i) diazotising an aromatic amine of Formula (2): ##STR6## to form the corresponding diazonium salt and coupling onto a compound of Formula (3): ##STR7## to form a compound of Formula (4): ##STR8## ii) diazotising the compound of Formula (4) and coupling onto a compound of Formula (5): ##STR9## to form the compound of Formula (1). In this process R, R₁ to R₆ and n are as hereinbefore defined.

The reactions leading to the formation of the present compounds may be performed under conditions that have been described in the art and the bisazo dyes may be isolated by known methods such as spray drying or precipitation followed by filtration.

According to a further feature of the present invention there is provided an ink composition comprising a bisazo dye of Formula (1) or salts thereof and a medium.

The present ink composition may comprise a mixture of two or more different dyes of Formula (1) or salts thereof or may comprise a mixture of one or more dyes of Formula (1) or salts thereof with one or more other dyes such as other azo dyes.

The medium for the present ink compositions may be a liquid or a low melting point solid. Liquid media may be aqueous or solvent-based. Aqueous-based ink compositions are generally used in office or home printers whereas solvent based ink compositions find use in industrial continuous printers.

It is preferred that the dye of Formula (1) is dissolved completely in the aqueous or solvent medium to form a solution.

Preferred ink compositions are those comprising a dye of Formula (1) and an aqueous medium.

The present bisazo dyes are particularly useful as colorants for aqueous inks. They exhibit high solubility in water and in aqueous media, rapid fixation and provide attractive black shades on plain paper.

The ink compositions of the present invention preferably contain from 0.5% to 20%, more preferably from 0.5% to 15%, and especially from 1% to 3%, by weight of the dye of Formula (1) based on the total weight of the ink. Although many ink compositions contain less than 5% by weight of colorant, it is desirable that the dye has a solubility of around 10% or more to allow the preparation of concentrates which may be used to prepare more dilute inks and to minimise the chance of precipitation of colorant if evaporation of the liquid medium occurs during use of the ink.

Where the liquid medium is aqueous based it is preferably water or a mixture of water and one or more water-soluble organic solvent, more preferably a mixture comprising water and from 1 to 10 water-miscible organic solvents. The weight ratio of water to organic solvent(s) is preferably from 99:1 to 1:99, more preferably from 99:1 to 50:50 and especially from 95:5 to 80:20. The water-soluble organic solvent(s) is preferably selected from C₁₋₄ -alkanols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, isobutanol or n-pentanol; amides such as dimethylformamide or dimethylacetamide; ketones or ketone-alcohols such as acetone or diacetone alcohol; ethers such as tetrahydrofuran or dioxane; oligo- or poly-alkyleneglycols such as diethylene glycol, triethylene glycol, hexylene glycol, polyethylene glycol or polypropylene glycol; alkyleneglycols or thioglycols containing a C₂ -C₆ -alkylene group such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol or hexylene glycol and thiodiglycol; polyols such as glycerol or 1,2,6-hexanetriol; C₁₋₄ -alkyl-ethers of polyhydric alcohols such as 2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol, 2- 2-(2-methoxyethoxy)ethoxy!ethanol, 2- 2-(2-ethoxyethoxy)-ethoxy!-ethanol, ethyleneglycolmonoallylether; heterocyclic ketones, such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone and 1,3-dimethylimidazolidone; sulphoxides such as dimethyl sulphoxide and sulpholane or mixtures containing two or more of the aforementioned water-soluble organic solvents, for example thiodiglycol and a second glycol or diethylene glycol and 2-pyrrolidone.

Preferred water-soluble organic solvents are 2-pyrrolidone; N-methyl-pyrrolidone; alkylene- and oligo-alkylene-glycols, such as ethyleneglycol, diethyleneglycol, triethyleneglycol; and lower alkyl ethers of polyhydric alcohols such as or 2-methoxy-2-ethoxy-2-ethoxyethanol; and polyethyleneglycols with a molecular weight of up to 500. A preferred specific solvent mixture is a binary or ternary mixture of water and diethylene glycol and/or, 2-pyrrolidone or N-methylpyrrolidone in weight ratios 75-95:25-5 and 60-80:0-20:0-20 respectively.

Examples of suitable ink media are given in U.S. Pat. No. 4,963,189, U.S. Pat. No. 4,703,113, U.S. Pat. No. 4,626,284 and EP 4,251,50A.

According to a further aspect of the present invention there is provided a process for printing a substrate with an ink composition using an ink-jet printer, characterised in that the ink composition comprises at least one dye of Formula (1) or salt thereof.

A suitable process for the application of an ink composition as hereinbefore described comprises forming the ink into small droplets by ejection from a reservoir through a small orifice so that the droplets of ink are directed at a substrate. This process is commonly referred to as ink jet printing, and preferred ink jet printing processes for the present inks are piezoelectric ink jet printing and thermal ink jet printing. In thermal ink jet printing, programmed pulses of heat are applied to the ink in the reservoir by means of a resistor adjacent to the orifice, during relative movement between the substrate and the reservoir.

The substrate used in the inkjet printing process may be paper, plastics, textile, metal or glass and is preferably paper, plastic or a textile material, especially a natural, semi-synthetic or synthetic material.

Examples of natural textile materials include wool, silk, hair and cellulosic materials, particularly cotton, jute, hemp, flax and linen.

Examples of synthetic and semi-synthetic materials include polyamides, polyesters, polyacrylonitriles and polyurethanes.

Preferred substrates include overhead projector slides or papers, including plain and treated papers, which may have an acid, alkaline or neutral character or textile materials such as cotton. An especially preferred substrate is paper.

The preferred ink compositions used in the process are as hereinbefore described.

According to a further aspect of the present invention there is provided a paper or an overhead projector slide or textile material printed with an ink composition characterised in that the ink composition comprises at least one dye of Formula (1) or salt thereof.

Where the liquid medium is solvent based the solvent is preferably selected from ketones, alkanols, aliphatic hydrocarbons, esters, ethers, amides or mixtures thereof. Where an aliphatic hydrocarbon is used as the solvent a polar solvent such as an alcohol, ester, ether or amide is preferably added. Preferred solvents include ketones, especially methyl ethyl ketone and alkanols especially ethanol and n-propanol.

Solvent based ink compositions are used where fast drying times are required and particularly when printing onto hydrophobic substrates such as plastics, metal or glass.

Where the medium for an ink composition is a low melting point solid the melting point of the solid is preferably in the range from 60° C. to 125° C. Suitable low melting point solids include long chain fatty acids or alcohols, preferably those with C₁₈₋₂₄ chains, or sulphonamides. The dye of Formula (1) or mixtures of dyes of Formulae (1) and (4) or mixture of dyes of Formulae (1) and (5) may be dissolved in the low melting point solid or may be finely dispersed in it.

According to a further aspect of the present invention there is provided a process for the coloration of a textile material with any of the abovementioned ink compositions which comprises the steps:

i) applying to the textile material by inkjet printing the ink composition; and

ii) heating the textile material at a temperature from 50° C. to 250° C. to fix the dye on the material.

The process for coloration of a textile material by inkjet printing preferably comprises a pre-treatment of the textile material with an aqueous pretreatment composition comprising a water-soluble base, a hydrotropic agent and a thickening agent followed by removing water from the pre-treated textile material to give a dry pre-treated textile material which is subjected to inkjet printing in step i) above.

The pretreatment composition preferably comprises a solution of the base and the hydrotropic agent in water containing the thickening agent.

The base is preferably an inorganic alkaline base, especially a salt of an alkali metal with a weak acid such as an alkali metal carbonate, bicarbonate or silicate or an alkali metal hydroxide. The amount of base may be varied within wide limits provided sufficient base is retained on the textile material after pretreatment to promote the dyeing of the pretreated textile material. Where the base is sodium bicarbonate it is convenient to use a concentration of from 1% to 5% by weight based on the total weight of the composition.

The hydrotropic agent is present to provide sufficient water to promote the fixation reaction between the dye and the textile material during the heat treatment, in step (d) above, and any suitable hydrotropic agent may be employed. Preferred hydrotropic agents are urea, thiourea and dicyandiamide. The amount of hydrotropic agent depends to some extent on the type of heat treatment. If steam is used for the heat treatment generally less hydrotropic agent is required than if the heat treatment is dry, because the steam provides a humid environment. The amount of hydrotropic agent required is generally from 2.5% to 50% by weight of the total composition with from 2.5% to 10% being more suitable for a steam heat treatment and from 20% to 40% being more suitable for a dry heat treatment.

The thickening agent may be any thickening agent suitable for use in the preparation of print pastes for the conventional printing of cellulose reactive dyes. Suitable thickening agents include alginates, especially sodium alginate, xantham gums, monogalactam thickeners and cellulosic thickeners. The amount of the thickening agent can vary within wide limits depending on the relationship between concentration and viscosity. However, sufficient agent is preferred to give a viscosity from 10 to 1000 mPa.s, preferably from 10 to 100 mPa.s, (measured on a Brookfield RVF Viscometer). For an alginate thickener this range can be provided by using from 10% to 20% by weight based on the total weight of the pretreatment composition.

The remainder of the pretreatment composition is preferably water, but other ingredients may be added to aid fixation of the dye to the textile material or to enhance the clarity of print by inhibiting the diffusion (migration) of dye from coloured areas to non-coloured areas before fixation.

Examples of fixation enhancing agents are cationic polymers, such as a 50% aqueous solution of a dicyanamide/phenol formaldehyde/ammonium chloride condensate e.g. MATEXIL FC-PN (available from ICI), which have a strong affinity for the textile material and the dye and thus increase the fixation of the dye on the textile material.

Examples of anti-migration agents are low molecular weight acrylic resins, e.g. polyacrylates, such as poly(acrylic acid) and poly(vinyl acrylate).

In the pretreatment stage of the present process the pretreatment composition is preferably evenly applied to the textile material. Where a deeply penetrated print or a deep shade is required the pretreatment composition is preferably applied by a padding or similar process so that it is evenly distributed throughout the material. However, where only a superficial print is required the pretreatment composition can be applied to the surface of the textile material by a printing procedure, such as screen or roller printing, ink jet printing or bar application.

In the pre-treatment stage of the present process, water may be removed from the pre-treated textile material by any suitable drying procedure such as by exposure to hot air or direct heating, e.g. by infra-red radiation, or micro-wave radiation, preferably so that the temperature of the material does not exceed 100° C.

The application of the ink composition to the textile material, stage (i) of the present process, may be effected by any ink jet printing technique, whether drop on demand (DOD) or continuous flow. The ink composition, preferably also contains a humectant to inhibit evaporation of water and a preservative to inhibit the growth of fungi, bacteria and/or algae in the solution. Examples of suitable humectants are, propan-1,2-diol, butan-1,2-diol, butan-2,3-diol and butan-1,3-diol. However, the presence of small amounts, up to about 10%, preferably not more than 5%, in total, of polyols having two or more primary hydroxy and/or primary alcohols is acceptable, although the composition is preferably free from such compounds. Where the ink jet printing technique involves the charging and electrically-controlled deflection of drops the composition preferably also contains a conducting material such as an ionised salt to enhance and stabilise the charge applied to the drops. Suitable salts for this purpose are alkali metal salts of mineral acids.

After application of the ink composition, it is generally desirable to remove water from the printed textile material at relatively low temperatures (<100° C.) prior to the heat applied to fix the dye on the textile material as this has been found to minimise the diffusion of the dye from printed to non-printed regions. As with the pretreated textile material removal of water is preferably by heat, such as by exposure to hot air or to infra-red or micro-wave radiation.

In stage (ii) of the present process, the printed textile material is submitted to a short heat treatment, preferably after removal of water by low-temperature drying, at a temperature from 100° C. to 200° C. by exposure to dry or steam heat for a period of up to 20 minutes. If a steam (wet) heat treatment is used, the printed material is preferably maintained at 100°-105° C. for from 5 to 15 minutes whereas if a dry heat treatment is employed the printed material is preferably maintained at 140°-160° C. for from 2 to 8 minutes.

After allowing the textile material to cool, unfixed dye and other ingredients of the pretreatment and dye compositions may be removed from the textile material by a washing sequence, involving a series of hot and cold washes in water and aqueous detergent solutions before the textile material is dried.

According to further aspects of the present invention there are provided textile materials, especially cellulosic textile materials, coloured with any of the ink compositions according to the present invention or by means of the process according to the present invention.

The invention is further illustrated by the following Examples in which all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1

Preparation of dye of Formula (1) in which n=1, R₆ =4-COOH, R₃ and R₄ ═OC₂ H₅, R₁ ═H and ##STR10##

4-Aminobenzoic acid (18.9 g) is added to water (1 l) and hydrochloric acid (42 cm³) added. After cooling to 0°-10° C. sodium nitrite (10 g) is slowly added and the solution stirred for 1 hr at 0°-10° C. Excess nitrous acid is destroyed by sulphamic acid and a solution of 2,5-diethoxyaniline (24.95 g) in ethanol (500 cm³) added below 10° C. Following dilution with water to a volume of ca 2.5 liters stirring is continued for several hours at room temperature. The product is isolated by filtration, washed with water and dried at 70° C. to give 53.3 g of a product having the following structure: ##STR11##

The monoazo product (28.3 g) is added to water (600 cm³) and the pH adjusted to 10 with sodium hydroxide solution. After screening, sodium nitrite (7 g) is added and the solution poured into a mixture of water (100 cm³) and hydrochloric acid (30 cm³) keeping the temperature at 20°-250° C. After stirring for 3 hrs excess nitrous acid is destroyed by sulphamic acid.

7-(2-Piperazinoethyl)amino-3-sulphonaphth-1-ol (30 g) is stirred in water (500 cm³) at 0°-10° C. and the pH adjusted to 10 by addition of sodium hydroxide. The above prepared diazonium salt suspension is slowly added at 0°-10° C. maintaining the pH at 9.5-10. After stirring for several hours at room temperature the solution is heated to 70° C. and ammonium chloride (150 g) added. The pH is slowly adjusted to 5 with hydrochloric acid and the product isolated by filtration at 60° C. and washed with ammonium chloride solution (10% w/v, 2 l). The filter cake is dissolved in water (1 l) by the addition of ammonia solution, heated to 70° C. and ammonium chloride (150 g) added. The pH is slowly adjusted to 1 with hydrochloric acid and the product again isolated by filtration at 70° C. washing with dilute hydrochloric acid (1 l). This procedure is carried out twice more before finally suspending the product in water (1 l) and adding ammonia solution until a homogeneous solution is obtained. The solution is dialysed to low conductivity and the product isolated by evaporation of the water to give 25.08 g of the desired product.

EXAMPLE 2

Preparation of dye of Formula (1) in which n=1, R₆ =4-COOH, R₃ and R₄ ═OC₂ H₅, R₁ ═H an R₂ =(4-carboxy)phenyl.

Prepared in analogous manner to example 1 replacing 7-(2-piperazinoethyl)amino-3-sulphonaphth-1-ol by 7-(4-carboxyphenyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 3

Preparation of a dye of Formula (1) in which n=1, R₆ =3-COOH, R₃ and R₄ ═OCH₃, R═H, R₂ =--CH₂ CH₂ N(CH₃)₂.

The general of Example 1 was repeated except that in place of 4-aminobenzoic acid there was used 3-aminobenzoic acid, in place of 2,5-diethoxyaniline there was used 2,5-dimethoxy aniline and in place of 7-(2-piperazinoethyl)amino-3-sulphonaphth-1-ol there was used 7-(2-dimethylaminoethyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 4

Preparation of a dye of Formula (1) in which n=1, R₆ =4-COOH, R₃ and R₄ ═OCH₃, R₁ ═H, R₂ ═CH₂ CH₂ N(CH₃)₂.

The general method of Example 1 was repeated except that in place of 2,5-diethoxyaniline there was used 2,5-dimethoxyaniline and in place of 7-(2-piperazinoethyl)amino-3-sulphonaphth-1-ol there was used 7-(2-dimethylaminoethyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 5

Preparation of a dye of Formula (1) in which n=1, R₆ =4-COOH, R₃ and R₄ =OCH₃, R₁ ═H ##STR12##

The general method of Example 1 was repeated except that in place of 2,5-diethoxyaniline there was used 2,5-dimethoxyaniline.

EXAMPLE 6

Preparation of a dye of Formula (1) in which n=1, R₆ =3-COOH, R₃ and R₄ ═OCH₃, R₁ ═H, R₂ =--CH₂ CH(NH₂)CH₃.

The general method of Example 1 was repeated except that in place of 2,5-diethoxyaniline there was used 2,5-dimethoxyaniline, in place of 4-aminobenzoic acid there was used 3-aminobenzoic acid and in place of 7-(piperazinoethyl)amino-3-sulphonaphth-1-ol there was used 7-(2-dimethylaminoethyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 7

Preparation of a dye of Formula (1) in which n=1, R₆ =3-COOH, R₃ and R₄ ═OCH₃, R₁ ═H, ##STR13##

The general method of Example 1 was repeated except that in place of 2,5-diethoxyaniline there was used 2,5-dimethoxyaniline, in place of 4-aminobenzoic acid there was used 3-aminobenzoic acid and in place of 7-(2-piperazinoethyl)amino-3-sulpho-1-naphthol there was use 7-(2-morpholinoethyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 8

Preparation of a dye of Formula (1) in which n=1, R₆ =3-COOH, R₃ and R₄ ═OCH₃, R₁ ═H, R₂ =--CH₂ CH₂ NHCH₂ CH₂ OH.

The general method of Example 1 was repeated except that in place of 2,5-diethoxyaniline there was used 2,5-dimethoxyaniline, in place 4-aminobenzoic acid there was used 3-aminobenzoic acid and in place of 7-(2-piperazinoethyl), amino-3-sulphonaphth-1-ol there was used 7-(2-(2-hydroxyethylamino)ethyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 9

Preparation of a dye of Formula (1) in which n=1, R₆ =4-COOH, R₃ and R₄ ═OCH₃, R₁ ═H, ##STR14##

The general method of Example 1 was repeated except that in place of 2,5-diethoxyaniline there was used 2,5-dimethoxyaniline and in place of 7-(2-piperazinoethyl)amino-3-sulphonaphth-1-ol there was used 7-(2-morpholinoethyl)amino-3-sulphonaphth-1-ol.

EXAMPLE 10

Ink compositions were prepared by dissolving 2 parts of the ammonium salt of each of the dyes in Examples 1 to 9 in 98 parts of a 90:10 mixture of water and 2-pyrrolidone. The ink compositions were printed onto plain paper using a thermal ink-jet printer to give black prints having good optical density, lightfastness and wetfastness.

EXAMPLE 11

The inks described in Tables I and II may be prepared wherein the Dye described in the first column is the Dye made in the above example of the same number. Numbers quoted in the second column onwards refer to the number of parts of the relevant ingredient and all parts are by weight. The inks may be applied to paper by thermal or piezo ink jet printing.

The following abbreviations are used in Table I and II:

PG=propylene glycol

DEG=diethylene glycol

NMP=N-methyl pyrollidone

DMK=dimethylketone

IPA=isopropanol

MEOH=methanol

2P=2-pyrollidone

MIBK=methylisobutyl ketone

P15=pentane-1,5-diol

BDL=butane-2,3-diol

CET=cetyl ammonium bromide

PHO=Na₂ HPO₄ and

TBT=tertiary butanol

TDG=thiodiglycol

                                      TABLE I     __________________________________________________________________________        Dye                    Na     Dye        Content            Water                PG                  DEG                     NMP                        DMK                           NaOH                               Stearate                                   IPA                                      MEOH                                          2P                                            MIBK     __________________________________________________________________________     1  2.0 80  5    6  4                 5     2  3.0 90    5  5     0.2     3  10.0            85  3    3  3             5   1     4  2.1 91    8                         1     5  3.1 86  5              0.2 4        5     6  1.1 81       9     0.5 0.5        9     7  2.5 60  4 15 3  3          6  10  5 4     8  5   65    20               10     9  2.4 75  5 4     5             6     5     1  4.1 80  3 5  2  10     0.3     1  3.2 65    5  4  6          5  4   6 5     2  5.1 96                        4     3  10.8            90  5                  5     4  10.0            80  2 6  2  5          1      4     5  1.8 80    5                       15     6  2.6 84       11                   5     7  3.3 80  2       10            2     6     8  12.0            90          7  0.3     3     9  5.4 69  2 20 2  1                 3 3     2  6.0 91       4                    5     __________________________________________________________________________

                                      TABLE II     __________________________________________________________________________        Dye     Dye        Content            Water                PG                  DEG                     NMP                        CET                           TBT TDG BDL                                      PHO 2P                                            PI5     __________________________________________________________________________     1  3.0 80  15      0.2               5     9  9.0 90    5                   1.2   5     3  1.5 85  5 5     0.15                           5.0 0.2     4  2.5 90    6  4                0.12     5  3.1 82  4 8     0.3                 6     6  0.9 85    10               5  0.2     7  8.0 90    5  5         0.3     8  4.0 70    10 4             1      4 11     9  2.2 75  4 10 3             2      6     1  10.0            91       6                    3     6  9.0 76    9  7     3.0        0.95                                          5     2  5.0 78  5 11                      6     3  5.4 86       7                    7     4  2.1 70  5 5  5  0.1                           0.2 0.1 5  0.1 5     3  2.0 90    10     1  2   88                 10     2  5   78       5         12         5     1  8   70  2    8         15         5     1  10  80                 8          12     1  10  80    10     __________________________________________________________________________ 

We claim:
 1. A bisazo dye of Formula (1) and salts thereof: ##STR15## in which R is H;one of R₁ and R₂ is H and the other is substituted C₁₋₄ -alkyl or substituted aryl wherein the substituents are selected from the group consisting of --NHC₁₋₄ -alkyleneOH, --NHC₁₋₄ -alkyl and ##STR16## R₃ and R₄ are each independently --OC₁₋₄ -alkyl; R₅ is H; R₆ is COOH; and n is 1, 2 or
 3. 2. A dye according to claim 1 provided that R₃ and R₄ are not both OC₂ H₅.
 3. A dye according to claim 1 wherein R₃ and R₄ are both OC₂ H₅.
 4. A dye according to any one of the preceding claims wherein n is
 1. 5. An ink composition comprising a liquid medium and a dye according to claim 1, 2 or
 3. 6. An ink according to claim 5 wherein the liquid medium comprises a mixture of water and one or more water-soluble organic solvents.
 7. An ink according to claim 6 wherein the water-soluble organic solvent is selected from the group consisting of C₁₋₄ -alkanols, ketone alcohols, ethers, oligo- and poly-alkylene glycols, alkylene glycols and thioglycols containing a C₂ -C₆ -alkylene group, polyols, C₁₋₄ -alkyl-ethers of polyhydric alcohols, heterocyclic ketones and sulphoxides and mixtures thereof.
 8. An ink according to claim 5 which contains 2-pyrrolidone, N-methyl-2-pyrrolidone, ethylene glycol, diethylene glycol, triethylene glycol, 2-methoxy-2-ethoxyethanol and/or a polyethylene glycol with a molecular weight of up to
 500. 9. An ink according to claim 5 which contains 2-pyrrolidone or N-methylpyrrolidone.
 10. A process for printing a substrate with an ink composition comprising forming the ink into small droplets by ejection from an reservoir through a small orifice so that the droplets of ink are directed at a substrate wherein said in composition comprises at least one dye according to claim 1, 2 or
 3. 11. A paper or an overhead projector slide or textile material printed with an ink composition wherein said ink composition comprises at least one dye according to claim 1, 2 or
 3. 12. A process for the coloration of a textile material with an ink composition comprising a dye according to claim 1, 2 or 3 which comprises the steps:i) applying the ink composition to the textile material by inkjet printing; and ii) heating the textile material at a temperature from 50° C. to 250° C. to fix the dye on the material.
 13. A textile material coloured with an ink composition of claim
 5. 14. A dye according to claim 1 wherein one of R₁ and R₂ is H and the other is selected from the group consisting of --CH₂ CH₂ NHCH₂ CH₂ OH, --CH₂ CH₂ NHC₁₋₄ -alkyl, CH₂ CH(NH₂)CH₃ ##STR17## 